CPCB Effluent Discharge Standards for Pulp and Paper Mills — Explained

About This CPCB Standard

Pulp and paper is one of the 17 industries designated as Grossly Polluting Industries (GPI) by CPCB. Discharge standards for pulp and paper mills are specified under Schedule I of the Environment (Protection) Rules 1986, notified under the Environment Protection Act 1986 (EPA 1986), and updated periodically through Gazette Statutory Rules (GSR notifications).

India has over 800 paper mills ranging from large integrated kraft pulp mills producing more than 100,000 tonnes per annum (TPA) to small agro-based units producing less than 10,000 TPA. CPCB standards account for this diversity: separate limits are prescribed for large integrated mills, small kraft mills, and agro-residue-based mills. Additionally, CPCB has established specific water consumption norms expressed in litres per tonne of paper produced, which are enforced alongside concentration-based discharge limits.

Pulp and Paper — Why It's a Priority Industry for CPCB

Paper mills generate between 50 and 200 cubic metres of wastewater per tonne of paper produced, depending on the process. The exact volume depends on the raw material (wood, agricultural residue, recycled fibre) and the pulping and bleaching technology used.

The key pollutant categories in paper mill effluent are:

• Lignin and lignin derivatives — the primary source of the characteristic dark colour and refractory (non-biodegradable) COD load in paper mill effluent. Lignin is separated from cellulose during pulping and, if not recovered, carries over into the wastewater stream.
• Cellulose fibres — contribute to Total Suspended Solids (TSS). These are relatively easier to remove by screening and sedimentation.
• Bleaching chemicals and chlorinated organics — when chlorine-based bleaching agents (Cl₂, hypochlorite, ClO₂) react with residual lignin in pulp, they produce Adsorbable Organic Halides (AOX) — a class of persistent, toxic, and potentially carcinogenic compounds.
• Organic acids and process chemicals — contribute to BOD. These are generally more amenable to biological treatment than the lignin-derived fraction.

Black liquor — the spent cooking liquor from the kraft (sulphate) pulping process — deserves special mention. Black liquor contains the bulk of the lignin dissolved during cooking and has an extremely high COD, typically exceeding 100,000 mg/L. It must be concentrated and incinerated in a chemical recovery boiler, never discharged into a drain or ETP. CPCB treats black liquor discharge as one of the most serious violations in the pulp and paper sector.

Pulp and Paper Effluent Discharge Limits at a Glance

The following table summarises the CPCB effluent discharge standards for pulp and paper mills under the Environment (Protection) Rules 1986. The threshold between large and small mills is set at 24,000 TPA of paper production.

In addition to concentration-based limits, CPCB prescribes specific wastewater generation norms (production-based volume limits):

• Large integrated kraft mills: ≤200 m³ per tonne of paper produced
• Agro-based mills: ≤150 m³ per tonne of paper produced
• Small paper mills: ≤100 m³ per tonne of paper produced

These volume norms are important because a mill can technically meet concentration limits by diluting its effluent — the production-based norms prevent this by controlling the total pollution load per unit of output.

AOX — The Adsorbable Organic Halides Parameter Explained

AOX (Adsorbable Organic Halides) is the parameter most specific to the pulp and paper industry. It is formed when chlorine-based bleaching chemicals — elemental chlorine (Cl₂), chlorine dioxide (ClO₂), or sodium hypochlorite (NaOCl) — react with the residual organic matter (primarily lignin) in pulp during the bleaching stage.

AOX compounds are a chemically diverse group of chlorinated organics. As a class, they are characterised by:

• Toxicity: many AOX compounds are acutely toxic to aquatic organisms
• Persistence: they are resistant to biological degradation and accumulate in sediments and organisms
• Carcinogenicity: certain chlorinated compounds in the AOX group, including dioxins and furans, are known or suspected carcinogens

The CPCB AOX limit is ≤5.0 kg per tonne of paper produced for large integrated mills. This is a production-based norm — not expressed per cubic metre of water — which means compliance is calculated by dividing total AOX discharged (measured in kg/day) by total paper production (tonnes/day). Measurement must be carried out by a NABL-accredited laboratory using APHA/ISO standard methods.

The primary route to AOX reduction is switching bleaching technology:

• Elemental Chlorine Free (ECF) bleaching — replaces elemental chlorine (Cl₂) with chlorine dioxide (ClO₂). ECF significantly reduces dioxin and furan formation and can achieve AOX well below 5 kg/tonne.
• Total Chlorine Free (TCF) bleaching — uses hydrogen peroxide (H₂O₂), ozone, or enzyme-based systems with no chlorine-containing compounds. TCF eliminates AOX formation entirely.

CPCB has mandated the adoption of ECF or TCF bleaching for large mills since 1999. Mills still operating elemental chlorine bleaching face both regulatory exposure and AOX compliance difficulty.

Colour in Paper Mill Effluent — Limits and Treatment

Paper mill effluent is characteristically dark — ranging from brown to near-black — due to lignin degradation products. These compounds are structurally similar to melanoidins and are among the most chemically stable organic molecules in industrial wastewater. They are highly resistant to conventional biological treatment (activated sludge, MBBR) because most microorganisms cannot metabolise them efficiently.

The CPCB colour limit is ≤200 Hazen units (Platinum Cobalt units, PCU), measured at 455 nm using a spectrophotometer per IS 3025 Part 4. This applies to both large and small mills.

Treatment options for colour removal, in order of increasing effectiveness:

• Coagulation with alum or PAC (Polyaluminium Chloride) — the most widely used primary treatment for colour. Effective for particulate and colloidal colour; typically achieves 50–60% colour reduction. Rarely sufficient on its own to meet the 200 Hazen limit for heavily coloured kraft mill effluent.
• Activated carbon adsorption — granular activated carbon (GAC) or powdered activated carbon (PAC) can adsorb dissolved colour compounds. Effective; can achieve ≤50 Hazen units. Higher operating cost due to carbon replacement or regeneration.
• Ozonation — ozone reacts with and degrades the conjugated chromophore structures in lignin-derived compounds, breaking the colour. Highly effective for lignin-based colour; also provides some disinfection benefit. Higher capital and energy cost than coagulation.

For most large integrated mills, a combination approach — biological treatment for BOD removal, followed by coagulation-flocculation, and a polishing step (activated carbon or ozone) — is required to achieve the 200 Hazen limit reliably.

Large Integrated Mills vs Small Agro-Based Units

The two broad categories of paper mills in India have meaningfully different pollution profiles and face different regulatory requirements.

Large integrated mills (more than 24,000 TPA): These are typically wood-based kraft mills or large integrated recycled fibre mills. They face the strictest standards: AOX limit of ≤5.0 kg/tonne, TSS limit of ≤100 mg/L, organochlorine limit of ≤1.0 kg/tonne, and mandatory Online Continuous Emission/Effluent Monitoring Systems (OCEMS). Chemical recovery is mandatory for kraft mills — the absence of a functioning chemical recovery boiler is itself a compliance violation, independent of discharge limits. These mills must also comply with production-based water consumption norms (≤200 m³/tonne for kraft).

Small agro-residue-based mills (up to 24,000 TPA): These mills, many clustered in Uttar Pradesh (particularly in the Muzaffarnagar area), use agricultural residues — paddy straw, bagasse, wheat straw — as raw material. They typically use the soda (alkali) pulping process rather than the kraft (sulphate) process. Since the soda process does not use sulphur compounds and the bleaching chemistry is different, these mills generally do not generate significant AOX. Accordingly, the AOX norm does not apply to small units. The TSS limit is slightly more lenient (≤150 mg/L vs ≤100 mg/L). However, CPCB surveys have consistently found high rates of non-compliance among small agro-based mills — particularly on BOD, COD, and colour limits — due to inadequate or poorly operated ETPs.

Monitoring and Testing Requirements

CPCB and SPCB monitoring requirements for pulp and paper mills are more demanding than for many other industries, reflecting GPI classification.

• OCEMS (Online Continuous Effluent Monitoring Systems): Large integrated mills are required to install and maintain OCEMS for pH, flow, and COD at the final discharge point. OCEMS data must be transmitted in real time to the CPCB/SPCB server. Tampering with OCEMS or data gaps are treated as violations.
• NABL-accredited lab testing: Quarterly minimum for large mills, covering the full suite of discharge parameters including AOX. Self-monitoring data must be submitted to the SPCB as required under Consent to Operate conditions.
• Production-based compliance verification: CPCB can verify compliance with production-based norms (AOX per tonne, water consumption per tonne) by cross-checking production records against effluent flow metering and lab data. This makes it difficult to argue compliance on concentration limits alone if total pollution load per tonne is excessive.
• Annual environmental audit: Required under the Environment (Protection) Act 1986 for scheduled industries. Results submitted to SPCB.
• Form V submission: Annual environmental statement under the Environment (Protection) Rules 1986, due by 31 January each year. Covers water consumption, effluent generation, treatment, and disposal for the preceding year.

Enforcement and Key NGT Orders

The pulp and paper sector has been subject to sustained enforcement attention from CPCB and the National Green Tribunal (NGT), driven primarily by the sector's impact on major river systems — particularly the Ganga and its tributaries.

Key enforcement dimensions:

• Ganga basin priority: CPCB has identified paper mills discharging to the Ganga basin as a priority enforcement category under the Namami Gange programme. Multiple mills in Uttar Pradesh have received closure notices or directions to upgrade treatment under this initiative.
• M.C. Mehta vs Union of India (Ganga pollution): This long-running Supreme Court case has resulted in several orders specifically identifying paper mills among the industries contributing to Ganga pollution. The case has driven significant regulatory action against mills in Uttarakhand and Uttar Pradesh.
• EP Act Section 15 penalties: Violations of effluent discharge standards under the Environment Protection Act 1986 attract imprisonment of up to five years and fines. Continuing violations after the first conviction attract enhanced penalties. CPCB can also issue directions under EP Act Section 5 requiring a unit to stop operations, disconnect power, or take specific corrective actions.
• Water Act Section 32 — Power disconnection: SPCBs have the authority under Section 32 of the Water (Prevention and Control of Pollution) Act 1974 to direct state electricity boards to disconnect power supply to non-compliant industrial units. This power has been used against paper mills in multiple states.
• NGT suo motu cognisance: The NGT has taken up cases involving river pollution from paper mills on its own initiative, particularly where CPCB or SPCB action has been seen as inadequate or slow. NGT orders can impose interim closures and require environmental compensation.

Mills that receive closure notices or show-cause orders face a short window to demonstrate compliance. The combination of OCEMS data, NABL lab reports, and production records means regulators can build a strong evidentiary case quickly. Early investment in adequate treatment and monitoring infrastructure is substantially less costly than enforcement action.